Carbon coating on lithium iron phosphate (LiFePO4): Comparison between continuous supercritical hydrothermal method and solid-state method

Title
Carbon coating on lithium iron phosphate (LiFePO4): Comparison between continuous supercritical hydrothermal method and solid-state method
Authors
홍승아김수진김재훈이병권정경윤이윤우
Keywords
Lithium iron phosphate; Carbon coating; Supercritical hydrothermal synthesis; Solid-state method
Issue Date
2012-08
Publisher
Chemical engineering journal
Citation
VOL 198-199, 318-326
Abstract
Carbon coating on lithium iron phosphate (LiFePO4) plays a crucial role in determining its electrochemical performance. This study investigates the effect of carbon coating on lithium iron phosphate particles synthesized using a continuous supercritical hydrothermal synthesis (SHS) method and a conventional solid-state (SS) method, with sucrose as a carbon precursor. The carbon content, carbon structure, morphology, electronic conductivity, and electrochemical performance of the carbon-coated LiFePO4 (C-LiFePO4) are characterized as a function of the following coating conditions: sucrose concentration, calcination temperature, and calcination time. The particles produced using supercritical water have a smaller size (400–1000 nm), larger BET surface area of 7.3 ㎡/g, and lower degree of particle aggregation compared with those produced via solid-state synthesis (particle size: 3–15 lm; BET surface area: 2.4 ㎡/g). The differences in the particle size and particle morphology of the LiFePO4 prepared using the two synthetic methods cause a significant difference in the uniformity of the carbon coating, carbon structure, and electronic conductivity. A more uniform carbon layer coating and greater amount of graphitic carbon are found in the LiFePO4 particles produced via the SS method. This leads to a higher discharge capacity of 147 mA h/g at a current density of 17 mA/g (0.1 C) after 30 cycles when compared with the C-LiFePO4 produced by the SHS method (135 mA h/g). No obvious capacity fading was observed. At a high current of 1700 mA/g (10 C), the delivered capacities of the C-LiFePO4 particles produced via the SS and the SHS methods are 55% and 52% of the theoretical value, respectively, at a carbon content of 6 wt.%. The carbon-coated samples prepared using the SHS and SS methods exhibit similar discharge capacity trends for the carbon content. As the carbon content increased to 6 wt.%,
URI
http://pubs.kist.re.kr/handle/201004/42817
ISSN
13858947
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KIST Publication > Article
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